Menambahkan view logic pada halaman utama

Menampilkan item ArrayList pada ListView

private void showTheDataIntoListview() {
        for (int i = 0; i < 20; i++) {
            todos.add("item todo - " + i);
        }
        todosAdapter.notifyDataSetChanged();
    }

Menambahakn event listener pada FloatingButton

...
fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent(MainActivity.this,AddItemActivity.class);
                startActivityForResult(intent,333);
            }
        });
...

kembalian

 protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(RESULT_OK==resultCode && requestCode==333){
            String item=data.getStringExtra("item");
            todos.add(item);
            todosAdapter.notifyDataSetChanged();
        }else{
            Snackbar.make(listView,"cancel",Snackbar.LENGTH_SHORT).show();
        }
    }

code keseluruhan

public class MainActivity extends AppCompatActivity {

    FloatingActionButton fab;
    ListView listView;
    ArrayList<String> todos=new ArrayList<>();
    ArrayAdapter<String> todosAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        setupView();
        setupViewListener();
        showTheDataIntoListview();
    }

    private void setupViewListener() {
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent(MainActivity.this,AddItemActivity.class);
                startActivityForResult(intent,333);
            }
        });
    }

    private void showTheDataIntoListview() {
        for (int i = 0; i < 20; i++) {
            todos.add("item todo - " + i);
        }
        todosAdapter.notifyDataSetChanged();
    }

    private void setupView() {
        fab = (FloatingActionButton) findViewById(R.id.fab);
        listView= (ListView) findViewById(R.id.listview);

        todosAdapter=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,todos);

        listView.setAdapter(todosAdapter);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(RESULT_OK==resultCode && requestCode==333){
            String item=data.getStringExtra("item");
            todos.add(item);
            todosAdapter.notifyDataSetChanged();
        }else{
            Snackbar.make(listView,"cancel",Snackbar.LENGTH_SHORT).show();
        }
    }
}